Effects Of Cu And Cr On Corrosion Resistance Of Zirconium Alloys

Zirconium alloy has a small thermal neutron absorption cross section,good mechanical properties and corrosion resistance.It is widely used for fuel cladding in nuclear reactors.The water-resistant side corrosion performance of zirconium alloy is the main factor affecting the service life of fuel elements.Alloying is an important way to improve the corrosion resistance of zirconium alloys.But there are lots of alloy elements in zirconium alloys,the interaction between each other is intricate,it is difficult to clarify the mechanism of interaction between alloy elements and alloy elements and water chemistry conditions.In this study,high-purity zirconium was used as base material to prepare Zr-x Cu-y Cr??x,y?=?0.3,0.2?,?0.3,0.5?,?0.3,1.0?,?1.0,0.0?,?1.0,0.2?,?1.0,0.5?,?0.0,1.0?,wt.%?)alloys,and through normalized processing and annealing at 600 ^?/5 h.The corrosion behavior of Zr-Cu-Cr series alloys were tested in static autoclave with superheated steam at 400 ^?/10.3 MPa and aqueous solution at360 ^?/18.6 MPa/0.01 M LiOH.The microstructure of the alloy substrate and oxide film was characterized by using SEM,EBSD and HRTEM,the influence of Cu and Cr on the microstructure and corrosion resistance of the zirconium alloy was studied to explore the corrosion mechanism,which provides experimental and theoretical basis for the practical application and development of new zirconium alloys.The main research results are as follows:For Zr-Cu-Cr alloys,when addition of Cu is 1.0 wt.%,the recrystallized grains of the alloy can be refined.When addition of Cr is 1.0 wt.%,abnormally large grains above40?m appear in the alloy.Zr-Cu-Cr alloys mainly contain Zr₂Cu phase above 100 nm and Zr Cr₂ phase below 80 nm.As the content of Cu increases,the number of Zr₂Cu increases.As the content of Cr increases,the size of Zr Cr₂ phase does not change obviously,but the number and distribution band density increase.The Cu element and the impurity Fe element tend to segregate in the Zr Cr₂ phase.The corrosion behavior of Zr-Cu-Cr series alloys in 400 ^?/10.3 MPa superheated steam shows that when the total content of Cu and Cr is less than 0.8 wt.%,The alloy has poor corrosion resistance.When the total content of Cu and Cr reaches 1.0 wt.%,The corrosion resistance of the alloy is better.Adding 1.0 wt.%Cr has better effects on improving the corrosion resistance of zirconium alloy than 1.0 wt.%Cu.This is mainly related to the second phase and the recrystallized grains.The corrosion law of Zr-Cu-Cr alloys in 360 ^?/18.6 MPa/0.01 M LiOH aqueous solution is different from that in the 400 ^?/10.3 MPa superheated steam.In general,the corrosion resistance is poor,and the corrosion transition occurs prematurely,which is mainly related to the reaction of the oxidation product of the Zr₂Cu phase with Li⁺or OH^-.Zr-0.3Cu-0.2Cr alloy has the best corrosion resistance,which is because the number of second phases in Zr-0.3Cu-0.2Cr alloy is little,and generate few defects during oxidation that stabilize the Zr O transition layer.Increasing the content of Cu and Cr deteriorates the corrosion resistance of the alloy,which is on account of the second phase in the alloy increases,and Zr₂Cu and Zr Cr₂ phases are likely to overlap or aggregate.The oxidation of these two second phases will promote each other,further accelerate corrosion.